I know this is a super old post but it might help someone else...
To calculate the burn time first weight your candle (container and all) and write this number down...
Burn your candle for a minimum of 3 hours ( to acheive full melt pool)
Weigh your candle again....
Take your Original Candle Weight
and minus the Weight after the 3 hour burn= X
Original Candle Weight x 3 (3 hour burn) and divide it by "X"
=Burn time in hours
Hope you understand this....